1. Field of the Invention
The present invention relates to a thin film transistor substrate and a fabricating method of the thin film transistor substrate, and more particularly to a fabricating method of a thin film transistor substrate that is adaptive for improving a yield of the thin film transistor substrate by use of a nanowire, and a thin film transistor substrate using the same.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) device controls a light transmittance of a liquid crystal by use of an electric field, thereby displaying a picture.
FIGS. 1 and 2 are respectively a perspective plan view and a cross sectional view representing a liquid crystal display panel of a related art.
Referring to FIGS. 1 and 2, the liquid crystal display panel includes a thin film transistor (hereinafter, referred to as “TFT”) substrate 70 and a color filter substrate 80 which face each other with a liquid crystal 16 therebetween.
The color filter substrate 80 includes a black matrix 18 which is formed on an upper substrate 11 at locations corresponding to gate lines 2 and data lines 4 crossing each other to define cell areas; a color filter layer 12 formed in the cell areas defined by the black matrix 18 for realizing color; and a common electrode 14 to form a vertical electric field with pixel electrodes 22.
The TFT substrate 70 of the liquid crystal display panel includes the gate lines 2 and the data lines 4 which are formed on a lower substrate 1 to cross each other with a gate insulating film 6 threbetween; a TFT 30 formed at each crossing part of the corresponding gate and data lines 2 and 4; a pixel electrode 22 formed in each cell area provided in the crossing structures of the gate lines 2 and the data lines 4.
For each TFT, the TFT 30 supplies a pixel signal of the corresponding data line 4 to the corresponding pixel electrode 22 in response to a gate signal of the corresponding gate line 2. To this end, the TFT 30 includes a gate electrode 32 connected to the gate line 2, a source electrode 34 connected to the data line 4, a drain electrode 36 connected to the pixel electrode 22 via a contact hole 48, and an active layer 38 which overlaps the gate electrode 32 and forms a channel between the source electrode 34 and the drain electrode 36. An ohmic contact layer 40 for being in ohmic contact with the source electrode 34 and the drain electrode 36 is formed on the active layer 38.
A plurality of thin films inclusive of the TFTs 30 of the TFT substrate 80 of the liquid crystal display panel are mainly formed by a photolithography process using a mask according to a related art. However, a study of forming the active layer 38 of the TFT 30 by use of a nanowire is being made.
FIG. 3 is a cross sectional diagram representing another example of a TFT substrate in the LCD panel of the related art.
Referring to FIG. 3, the TFT substrate of the related art includes the active layer 38 of the TFT formed by use of a nanowire 39. The TFT substrate of FIG. 3 is the same as the TFT substrate of FIG. 2, except that the active layer 38 of the TFT is formed by use of the nanowire 39. Thus the explanation for the same elements will be omitted.
The nanowire 39, which forms the active layer 38 of the TFT, is formed in a structure, as shown in FIG. 4, where an inorganic and organic insulator 39B encompasses a semiconductor material 39A.
As shown in FIGS. 5A and 5B, the active layer 38 of FIG. 3 is formed by use of the nanowire 39, which is scattered over the gate electrode 32 where the gate insulating film 6 is spread, specially over a location where the active layer 38 of the TFT is to be formed after randomly scattering the nanowire 39 on the lower substrate 1 where the gate electrode 32 and the gate insulating film 6 are formed.
However, the formation of the active layer 38 of the TFT by use of the nanowire 39 has a disadvantage in that the yield of the TFT substrate is decreased, because the nanowire 39 is not correctly placed on a right location where the active layer 38 is to be formed since the nanowire 39 is randomly scattered on the lower substrate 1 in order to form the active layer 38 of the TFT. For example, as in FIGS. 5A and 5B, there arises a problem that the nanowire 39 is wasted because the nanowire 39 is scattered and provided at an arbitrary location (A) other than a location where the active layer 38 of the TFT is to be formed. Also the nanowire 39 may not be aligned with the gate electrode as shown in “B” of FIG. 5B. Consequently, there arises a problem that the lower substrate 1 cannot be used, because it includes the nanowire 39 scattered in areas other than the locations where the active layer 38 of the TFT is to be formed.
In order to address these problems, there has been proposed a method that the nanowire 39 is spread over only the area where the active layer 38 of the TFT is to be formed on the lower substrate 1 by use of an inkjet. In this method, the nanowire 39 is spread by use of the inkjet over an area where the active layer 38 of the TFT on the lower substrate 1 is to be formed, after dissolving the nanowire 39 in an alcohol system solvent such as ethanol, methanol, etc. However, in this case, the alcohol system solvent in which the nanowire 39 is dissolved has a problem of being spread to an area other than an area where the nanowire 39 is spread (i.e., an area other than an area where the active layer 38 of the TFT is to be formed) due to its characteristic. Because of this feature, there is a problem in that the yield of the TFT substrate formed by the related art method is decreased due to a patterning defect of the active layer 38 of the TFT.